Light receiving circuit, optical transceiver, and received output waveform cross point controlling method

Abstract

A light-receiving circuit includes an optical-to-electrical transduction element, a TIA processing section to output a voltage in proportion to a current input from the optical-to-electrical transduction element, and a control section to control the TIA processing section. The TIA processing section includes a TIA, which generates the voltage output signal in proportion to the current input from the optical-to-electrical transduction element, an amplifier, which amplifies the output signal of the TIA, a monitoring portion, which monitors the current to be input to the TIA, and an offset-adjusting portion provided between the TIA and the amplifier to adjust and output an offset level of the output signal of the TIA to the amplifier. The control section acquires a value of the current to be input from the monitoring portion to the TIA, and controls the offset-adjusting portion so as to adjust the offset level in proportion to that acquired current value.

Description

[0001]The present application is based on Japanese patent application No. 2014-134197 filed on June. 30, 2014, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]This invention relates to a light receiving circuit, an optical transceiver and a received output waveform cross point controlling method.DESCRIPTION OF THE RELATED ART[0003]As a light receiving circuit provided in an optical transceiver and the like, a light receiving circuit comprising a photoelectric conversion element such as a photodiode (PD) which transduces an input optical signal into an electrical signal, and a transimpedance amplifier processing section (hereinafter, referred to as “TIA processing section”) which outputs a voltage in proportion to an electric current input from the photoelectric conversion element has been known.[0004]In general, the term “transimpedance amplifier (hereinafter, referred to as “TIA”)” refers either to only an electric current to volta...

AI Technical Summary

Benefits of technology

This configuration effectively regulates cross points of the received output waveform within the desired range, even under high light input conditions, preventing saturation and maintaining sensitivity, regardless of the presence of automatic gain control or cross point correction functions.

Problems solved by technology

For that reason, the conventional light receiving circuit has the following drawback: When a light input much higher than its receiving sensitivity is input, its received output waveform is saturated and distorted, and therefore cross points of that received output waveform greatly deviate from 50 percent.

More specifically, when the high light input is input, the difference in offset between the differential signal pair is large, distortion occurs in differential signals output by the TIA, and the cross points of the received output waveform greatly deviate from 50 percent.

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